Finasteride or dutasteride. They control BPH perfectly, while also treating male pattern baldness. Combine with daily tadalafil to offset any chance of the dubious sexual side effects, while also reducing gynecomastia (it's also an aromatase inhibitor!). Make sure to have regular 5ari-aware PSA screenings to make sure high grade cancers are caught and you are golden.
fin/dut + tad are my favorite medications to keep men fresh for many more years than intended by nature.
Have your children before you start though, as dut will probably make you sterile eventually.
I've personally had very little luck with official channels there. Most won't prescribe anything for hair loss, several dermatologists said to just get used to it, one would prescribe fin pills, i.e. systemic - which did eventually give me pain in the breast tissues (so I ceased using it), but not topical, citing that it's too new on the market. I was unable to find anyone who would or even could look at serum DHT. I eventually settled on just paying one of these apparently legal telemedicine vendors 20 bucks per topical fin prescription.